Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 14, 2008
Publication Date: February 1, 2009
Citation: Barkley, N.L., Pinnow, D.L., Wang, M.L., Pederson, G.A. 2009. First Report of Tomato Spotted Wilt Virus Infecting African Clover (Trifolium tembense) in Georgia. Plant Disease. 93(2):202. Interpretive Summary: Tomato spotted wilt virus (TSWV) is classified as a Tospovirus that infects a broad range of plant hosts. The virus is known to be transmitted by tiny insects known as thrips when the larvae feed on infected host plants. This virus causes disease in many economically important agricultural crops such as peanuts, tomatoes, and peppers and generally results in significant yield loss for farmers. Controlling the spread of this disease is challenging and currently limited strategies are available to prevent and control the dissemination of this disease except for early diagnosis and destruction of infected material. In 2008 an African clover classified as Trifolium tembense was being regenerated in a greenhouse in Georgia. Visual inspection of the plants demonstrated that they could possibly be infected with TSWV. This was later confirmed by performing two separate diagnostic tests to validate the presence of the virus within 26 individuals of Trifolium tembense. The tests revealed that all but 2 accessions were infected with TSWV. This is the first known report of an African clover infected with TSWV.
Technical Abstract: Tomato spotted wilt virus (TSWV) causes a destructive disease which affects many economically important host plants. TSWV has been reported in subterranean clover (Trifolium subterraneum), white clover (Trifolium repens), and various unidentified wild clovers (Trifolium spp). in North America and Australia (Bitterlich & MacDonald, 1993; Wilson, 1998), but never before in an African species. Trifolium tembense, an herbaceous annual African clover which is mainly used for grazing or pasture improvement, is part of the national germplasm collection housed at the Plant Genetic Resources Conservation Unit in Griffin, Georgia. TSWV was found naturally infecting several accessions of this species being grown for regeneration in a greenhouse in 2008. Initial putative identification of the virus was done by visual inspection of host symptoms, which included ringspots, necrotic and chlorotic local lesions, and sometimes mild systemic wilting. This was subsequently confirmed by DAS-ELISA and reverse transcription-PCR (RT-PCR). The primers (5’-ATGTCTAAGGTTAAGCTC-3’ forward and 5’-TTAAGCAAGTTCTGTGAG-3’ reverse) targeted the nucleocapsid gene of TSWV and amplified an expected product of approximately 800 bp (Holguín-Peña & Rueda-Puente, 2007). A total of 26 individuals representing 12 plant accessions were screened for TSWV. All but two accessions tested positive for the virus. The RT-PCR data substantiated the ELISA results and confirmed the suspected infection. Over 26% of the samples infected by TSWV were further characterized by purifying and sequencing (bidirectionally) the RT-PCR product. The resulting sequences were aligned and edited using AlignIR. Over 700 bp of sequence data was compiled and displayed 98% identity with deposited TSWV nucleocapsid gene sequences in GenBank, with no similarity to any other targets. As far as the authors are aware, this is the first report of TSWV infection in Trifolium tembense. Accessions potentially resistant to TSWV within this species were identified and need to be further substantiated.